In recent years, it is designed to attain miniaturization and density growth of electronic equipment by integrating a passive part such as a capacitor or inductor which was conventionally mounted on a ceramic substrate surface into a ceramic multilayer substrate. Such a ceramic multilayer substrate is produced by forming a green sheet from a slurry of a dielectric porcelain composition and an organic solvent by doctor blade method followed by drying, printing a wiring conductor on the top surface of the sheet, forming a laminated body by laminating such green sheets of the same dielectric porcelain composition as described above, and co-firing it.
Such a ceramic multilayer substrate uses Ag or Cu with small specific resistance as the wiring conductor for performing high-performance signal processing at high speed. Therefore, various ceramic materials which can be co-fired with Ag and Cu at temperatures lower than 962° C. that is the melting point of Ag and 1084° C. that is the melting point of Cu are developed.
In the above-mentioned ceramic multilayer substrate, a one having a dielectric constant of 10 or less is suitably used for suppressing stray capacitance or coupling capacitance between wires. While, when a capacitor is formed within the ceramic multilayer substrate, it is desirable for the ceramics constituting the capacitor to have a high dielectric constant.
The barium titanate-based dielectric porcelain composition generally has a high dielectric constant, and can form a high-capacity capacitor within the ceramic multilayer substrate. However, since it needs a sintering temperature as high as 1150 to 1200° C. or higher, Ag and Cu cannot be used as the wiring conductor to be co-fired. Therefore, it is necessary for the barium titanate-based dielectric porcelain composition to be sinterable at a temperature of 1000° C. or lower while having practical dielectric constant and dielectric loss.
On the other hand, in use as a piezoelectric element, development of a piezoelectric material having a lead-free composition is demanded since conventional PZT contains lead that is an environmental load substance, and the barium titanate-based porcelain composition is attracting attention as a candidate thereof.
Further, in use as a laminated piezoelectric element through molding of sheets by the doctor blade method, it is important to develop a low-temperature sintering technique capable of suppressing use of expensive Pt or Pd. However, lead-free piezoelectric porcelain compositions disclosed in the past need firing temperatures of 1000° C. or higher.
Various prior literatures are known for the barium titanate-based dielectric porcelain composition. In Japanese Patent Application Laid-Open No. Hei 5-120915A, lead is added to allow low-temperature firing.
Japanese Patent Application Laid-Open No. Sho 54-53300A describes addition of copper oxide and bismuth oxide.
Japanese Patent Application Laid-Open No. Sho 61-251561A describes addition of copper oxide.
Further, in Japanese Patent Application Laid-Open Nos. 2001-143955A, 2000-226255A, 2000-264724A and 2003-335575A, barium titanate-based dielectric porcelain compositions are disclosed.
Lead-free piezoelectric porcelain compositions are disclosed, for example, in Japanese Patent Application Laid-Open Nos. Hei 11-228226A, Hei 11-228228A, and Hei 10-297969A, Japanese Patent No. 2942535A, and Japanese Patent Application Laid-Open Nos. Hei 11-29356A, 2002-160967A and 2002-265262A.